Significance: Outcomes for patients with pre-B ALL have substantially improved over the past decades. However, this is not the case for 15-20% of children who relapse after initially successful treatment. With current algorithms of risk stratification, these patients are undistinguishable from patients who respond well to standard chemotherapy. As a consequence, most patients with pre-B ALL relapse will die from their disease, while others suffer long-term sequelae from unnecessary toxicity. This proposal is based on the central observation that relapse clones in B cell lineage leukemia are resistant to conventional chemotherapy but uniquely vulnerable to perturbations of glucose and energy metabolism. Therefore, agents that specifically target B cell-intrinsic metabolic liabilities may improve outcomes for patients with relapse leukemia without adding substantive toxicity to the treatment regimen. Rationale and Innovation: Unlike other cell types, (pre-) B cells are selected for an intermediate level signaling strength. Critical survival and proliferation signals emanate from the pre-B cell receptor (pre-BCR): Both attenuation below minimum (e.g. non-functional pre-BCR) and hyperactivation above maximum (e.g. autoreactive pre-BCR) thresholds of signaling strength trigger negative selection and cell death. We recently discovered that pre-B ALL, including relapse ALL, is bound by the same rules that also govern normal B cell selection (Swaminathan et al., Nature Medicine 2013). Despite oncogenic transformation, we found that basic mechanisms of negative selection are still functional in pre-B ALL. Recent studies by our group demonstrated that pharmacological hyperactivation of the pre-BCR tyrosine kinase SYK engages a deletional checkpoint, which is functionally equivalent with negative selection of autoreactive B cells. In preliminary studies for this proposal, we found that cell death in response to SYK hyperactivation is caused by acute energy depletion and exhaustion of glycolytic reserves of B cell lineage ALL cells. This proposal is based on the central observation that relapse clones in B cell lineage leukemia are resistant to conventional chemotherapy but uniquely vulnerable to perturbations of glucose and energy metabolism. Hypotheses: Based on these and other findings, we are proposing three new lines of investigation to be developed over the next seven years. This will allow us to test and refine this emerging concept for the treatment of B-lineage ALL relapse in a pre-clinical setting. (1) Relapse pre-B ALL cells frequently acquire deletions of B cell-specific transcription factors PAX5, and IKZF1, the functional significance of which is not known. Here we test the hypothesis that these lesions reduce stringency of B cell lineage commitment and thereby in part mitigate B cell intrinsic liabilities of glucose and energy metabolism. (2) Recent studies by our group revealed that pre-B ALL cells are uniquely addicted to inhibitory regulators of Syk-mTOR signaling (Shojaee et al., Cancer Cell 2014; Chen et al., Nature 2014). Here we test the hypothesis that signaling inhibitors protect pre-B ALL cells from energy depletion and exhaustion of glycolytic reserves and, hence, engagement of a deletional checkpoint, that is functionally equivalent with negative selection of self-reactive B cells. (3) Glucocorticoids are highly effective in killing both pre-B LL cells and self-reactive B cell clones in autoimmune diseases. Compared to any other cell types, B cell lineage cells are >75-fold more sensitive to glucocorticoids. Here we hypothesize that glucocorticoids, by inhibiting glucose uptake and glycolysis, cause acute energy depletion and, hence, exacerbate B cell-intrinsic metabolic liabilities.